Metal-ceramic composites may find a wide variety of uses where certain physical characteristics play an important role in their use. For example, in many instances it is desirable that the article which is employed for particular purposes possess a low thermal coefficient of expansion. In addition to this desirable characteristic, it is also important that materials which may be used as valve seats, pumps, let-down valves, fluid bed units, lock hoppers, etc. also possess a high degree of strength as well as resistance to wear in order to combat or overcome the problems which arise in areas concerned with various deleterious effects such as wear or erosion.
In many instances where the metal articles possess relatively complex or convoluted shapes, it has been necessary to cast the material in a rough form, following which the desired final configuration with attendant tolerances is attained by machining the article. However, with the advent of powder metallurgy followed by a subsequent sintering operation, the obtention of the desired articles with the final shape can be obtained with a corresponding economical advantage over conventional casting and machining techniques, a portion of the economical advantage being attributable to the elimination of an extensive machining operation.
In many instances composites of metals and ceramics are relatively porous in nature with a concurrent relatively low density. These characteristics lead to inherent disadvantages in the finished article in that the articles will not possess a high strength which is necessary for any applications in which the article is to be used. It is therefore necessary to subject these composites to a sintering technique. The sintering process involves a partial welding together of powder particles at temperatures below the melting point thereof and may occur in powder metallurgy with or without the presence of a liquid. The combination of heat and/or pressure during this process will result in the obtention of mixtures which will possess a low porosity with a concurrent densification to produce greater strength, conductivity and, as hereinbefore set forth, density.
Normally speaking, iron powder and silicon carbide powder when in admixture and porous possess a relatively low density and will not sinter readily to form a composite which possesses a high density. This is also true in other metal powder-ceramic composites such as aluminum-silicon carbide, magnesium-silicon carbide, etc. In order to obtain composite articles which are relatively nonporous and possess a high density as well as eliminating the problem of segregation of the ceramic particles to provide a better control of homogeneous distribution of the particles and a metallic microstructure, it is necessary to provide some process for enhancing the sintering of the composite to produce a composite which will not crumble when subjected to strain or pressure but will retain its desired form or configuration, will not be subject to wear or erosion and thus will provide a useable article of manufacture.